Preparation of ketorolac

ABSTRACT

5-Benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxamides of the formula                    
     where R 1  is alkyl and R 2  is optionally substituted phenyl; and the method for their preparation and their conversion to ketorolac and its pharmaceutically acceptable salts.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims the benefit under 35 USC120 and 121 of, U.S. application Ser. No. 09/460,526, filed Dec. 13,1999, now U.S. Pat. No. 6,197,976. Application Ser. No. 09/460,526 inturn claims the priority under 35 USC 119(e) of Provisional ApplicationNo. 60/112,386, filed Dec. 14, 1998. These two applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of ketorolac and itspharmaceutically acceptable salts, especially the trometharnine salt.

U.S. Pat. No. 4,089,969 (to Syntex (U.S.A.) Inc.) discloses various5-(optionally substitutedbenzoyl)-2,3-dihydro-1H-pyrrolizine-1-carboxylic acids, includingketorolac, (±)-5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acid,of formula I,

the tromethamine salt of which is the active ingredient of theanti-inflammatory and analgesic drugs TORADOL® and ACULAR®.

Various methods for the preparation of ketorolac and relatedpyrrolizine-1-carboxylic acids are exemplified in the patent andchemical literature, and many proceed through a common intermediate,2,3-dihydro-1H-pyrrolizine-1-carboxylic acid, or its alkyl esters. Thealkyl esters may be readily 5-aroylated by methods known to the art,e.g. by Vilsmeier-Haack or Friedel-Crafts aroylations, as described inU.S. Pat. Nos. 4,089,969 and 4,347,186 (also to Syntex (U.S.A.) Inc.),both using dialkylamides; U.S. Pat. No. 4,353,829 (also to Syntex(U.S.A.) Inc.), using morpholides; and in U.S. Pat. No. 4,496,741 (toMerck); and the resulting ester saponified by conventional methods toyield a 5-aroyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acid.

U.S. Pat. No. 4,874,871 (also to Syntex (U.S.A.) Inc.) discloses amethod of preparing 2,3-dihydro-1H-pyrrolizine-1-carboxylic acid andrelated compounds from pyrrole in the following manner:

where X and X′ are independently halogen;

Y is —OH; —OM⁻M⁺, wherein M is an alkali metal; or —NRR′ (where R islower alkyl and R′ is lower alkyl or aryl, or —NRR′ is the residue of asaturated cyclic amine); and

Z is Li, MgCl, or MgBr.

According to U.S. Pat. No. 4,874,871, the(±)-2,3-dihydro-1H-pyrrolizine-1-carboxamides or salts may be hydrolyzedto the corresponding acid and then converted to the corresponding estersby conventional means; and the esters 5-aroylated and hydrolyzed toafford 5-aroyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acids by themethods described in U.S. Pat. Nos. 4,089,969; 4,347,186; and 4,353,829.

The disclosures of these patents, and other patents and articlesreferred to throughout this specification, are incorporated herein byreference.

SUMMARY OF THE INVENTION

In a first aspect, this invention includes5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxamides of Formula 6,

where R¹ is alkyl; and R² is optionally substituted phenyl.

In a second aspect, this invention includes a method of preparing the5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxamides of Formula 6.

In a third aspect, this invention includes a method of preparingketorolac and its pharmaceutically acceptable salts, comprisingpreparing 5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxamides of Formula6, followed by hydrolysis, optionally followed by formation of apharmaceutically acceptable salt.

In a fourth aspect, this invention includes a method of preparing thepyrrolylbutanamides of Formula 3.

In a fifth aspect, this invention includes an improved method ofpreparing the 2,3-dihydro-1H-pyrrolizine-1-carboxamides of Formula 4.

The preparation may be represented schematically:

where R¹ is alkyl;

R² is optionally substituted phenyl;

R³ is Cl or —NR⁴R⁵ (where R⁴ and R⁵ are independently C₃₋₈ alkyl, or—NR⁴R⁵ is morpholino, piperidino, or pyrrolidino); and

X is Cl or Br.

DETAILED DESCRIPTION OF THE INVENTION Definitions

Unless otherwise stated, the following terms used in the specificationand claims have the meanings given below:

“Alkanol” means C₁₋₄ alcohols such as methanol, ethanol, propanol,isopropanol or butanol. A preferred alkanol is methanol.

“Alkyl” means a straight, branched, or cyclic saturated monovalenthydrocarbon radical having from one to eight carbon atoms, e.g. methyl,ethyl, isopropyl, cyclopropyl, cyclopropylmethyl, and the like. “Loweralkyl” means C₁₋₄ alkyl. “Lower alkoxy” means —OR where R is loweralkyl.

“Grignard solvent” means a solvent suitable for the formation ofGrignard reagents or their reaction with other reagents. “Grignardsolvent” includes ethers such as tetrahydrofuran and diethylene glycoldibutyl ether (butyl diglyme), which may be used as sole solvents,especially in the formation of the pyrrole Grignard reagent of formula1, and mixtures of such suitable sole solvents, especiallytetrahydrofuran, with aprotic cosolvents such as hydrocarbon solvents,e.g. toluene, or polar aprotic solvents such as acetonitrile,N,N-dimethylformamide, N-methyl-2-pyrrolidinone (NMP),tetramethylethylenediamine,1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU),1,3-dimethyl-2-imidazolidinone (DMEU), or ethylene glycol diethers, e.g.1,2-dimethoxyethane (glyme), diethylene glycol dimethyl ether (diglyme),diethylene glycol diethyl ether, triethylene glycol dimethyl ether(triglyme), tetraethylene glycol dimethyl ether (tetraglyme), which maybe used either in the formation of the pyrrole Grignard reagent offormula 1 or, especially, in the formation of the pyrrolylbutanamide offormula 2. Butyl diglyme may be used as a sole solvent in the formationof the pyrrole Grignard reagent and used without addition of aproticpolar cosolvents in the formation of the pyrrolylbutanamide. A preferredcosolvent for tetrahydrofuran is diglyme.

“Hydrocarbon solvent” means aliphatic or aromatic hydrocarbon solventssuch as hexane, cyclohexane, toluene, and the like.

“Optionally substituted phenyl ” means phenyl optionally substitutedwith one to three lower alkyl, lower alkoxy, nitro, fluoro, chloro,bromo, or trifluoromethyl substituents.

“Organic solvent” includes the hydrocarbon solvents mentioned above andalso includes esters such as ethyl acetate and the like, chlorinatedhydrocarbons such as dichloromethane and the like, and the polar aproticsolvents mentioned above.

“Strong base” refers to bases such as alkali metal hydroxides, loweralkoxides, and the like, especially the alkali metal hydroxides.

When a solvent is described as being of a particular type, such as a“Grignard solvent”, the term includes not only a “Grignard solvent” asdefined, but in addition solvent mixtures containing a Grignard solventand minor proportions of other solvents (e.g. hydrocarbon solvents),provided that the solvent properties are primarily determined by thetype of solvent named.

Starting Materials and Purification

The starting pyrrole and the compounds of formula 2, 3, 4, and 6 may beisolated and purified, if desired, or may be carried into the nextreaction step by removing the solvent, using conventional techniquesincluding but not limited to filtration, distillation, crystallization,chromatography, and the like. The compounds may be characterized usingconventional means, including physical constants and spectralcharacteristics. The product ketorolac and its pharmaceuticallyacceptable salts may be isolated, purified, and characterized similarly.

Compounds 2. The N-alkyl-N-aryl-2-bromo-4-chlorobutanamides of formula 2may be prepared by methods known to the art. See, for example, WestGerman Patent No. 804 567 (BASF), for the preparation of2-bromo-4-chlorobutanoyl chloride from α-bromo-γ-butyrolactone.2-Bromo-4-chlorobutanoyl bromide may be prepared by the bromination of4-chlorobutanoyl chloride with bromine, as shown in the Example. Seealso U.S. Pat. No. 4,874,871, referred to previously, for thepreparation of the butanamides from the butanoyl halides.

An N-alkyl-arylamine is treated with a 2-bromo-4-chlorobutanoyl halidein the presence of a tertiary amine base such as a trialkylamine and anorganic solvent such as toluene. The reaction temperature is maintainedat about 10° C. to 80° C. while the addition is allowed to proceed tocompletion in about 10 minutes to 10 hours. The resultingdihalobutanamide (2) may be isolated by conventional techniques, such asaddition of water and acidification of the solution with mineral acid,e.g. hydrochloric acid, separation of the organic and aqueous layers,and evaporation of the solvent; and is used either with or withoutfurther purification in Step 2.

The Process

In Step 1, pyrrole is converted to a pyrrole Grignard reagent of formula1 by methods well known to the art, such as by the reaction of pyrrolewith an alkylmagnesium halide such as methylmagnesium chloride, insolution in a Grignard solvent, e.g. tetrahydrofuran or diethyleneglycol dibutyl ether. Each of these reagents, for example, iscommercially available from suppliers such as Aldrich or Ferro. Thereaction is generally performed at reduced temperatures and under aninert atmosphere, e.g. nitrogen, and occurs rapidly, typically within 10minutes. The resulting pyrrole Grignard reagent (1) is generally usedimmediately in Step 2.

In Step 2, the dihalobutanamide (2) is contacted with the pyrroleGrignard reagent (1) from Step 1 until the reaction to theN-alkyl-N-aryl-4-chloro-2-(2-pyrrolyl)butanamide of formula 3 iscomplete. The pyrrole Grignard reagent (1) is preferably present inexcess, for example between 1.2-fold and 3-fold excess, typically abouta 2-fold excess, over the dihalobutanamide (2) to minimize the formationof 2,5-disubstituted pyrrole products. The reaction is generallyperformed under an inert atmosphere by the addition of a solution of thedihalobutanamide (2) to a stirred solution of the pyrrole Grignardreagent (1) in a suitable solvent, typically the solvent in which it wasformed: however, if the pyrrole Grignard reagent (1) was formed intetrahydrofuran, desirably a cosolvent is added. The dihalobutanamide(2) may be added to the pyrrole Grignard reagent (1) as a neat material,or as a solution in an organic solvent such as toluene. Preferably, thepreparation of the pyrrole Grignard reagent (1) and the alkylationreaction of Step 2 both take place in butyl diglyme, where thealkylation reaction may be accomplished at higher concentrations andsolvent recycle is simplified to a single solvent. The reactiontemperature may be from about 0° C. to 60° C., but the reaction isslowed by cooling, and addition typically takes place near roomtemperature, e.g. between about 25° C. and 30° C., in one or moreportions, after which the reaction is allowed to proceed to completion.The reaction time may range from 30 minutes to 48 hours, but isordinarily 2 hours to 10 hours. Following completion of the reaction,the resulting pyrrolylbutanamide (3) may be isolated by conventionaltechniques, such as addition of water and acidification of the solutionwith mineral acid, e.g. by addition of concentrated hydrochloric acid topH 1, followed by separation of the organic and aqueous layers. Theorganic layer is treated with base, concentrated under reduced pressure,and filtered; and may be used directly in Step 3.

In Step 3, the pyrrolylbutanamide (3) is cyclized to the correspondingN-alkyl-N-aryl-2,3-dihydro-1H-pyrrolizine-1-carboxamide of formula 4.The treated organic layer from Step 2 is added to a stirred suspensionof a strong base such as an alkali metal hydroxide, in the presence of aphase transfer catalyst such as ALIQUAT® 336 (tricaprylylmethylammoniumchloride) or other quaternary ammonium salt, and a hydrocarbon solventsuch as toluene. The reaction temperature is maintained at about 10° C.to 100° C., typically under an inert atmosphere, while the cyclizationis allowed to proceed to completion in about 10 minutes to 48 hours. Thepyrrolizinecarboxamide (4) may then be recovered by addition of water,separation of the layers and subsequent crystallization from the organiclayer.

In Step 4, theN-alkyl-N-aryl-5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxamides offormula 6 are prepared by 5-aroylation methods known to the art, e.g. bythe modified Vilsmeier-Haack aroylations described in U.S. Pat. Nos.4,089,969 and 4,347,186 (using dialkylamides) and U.S. Pat. No.4,353,829 (using morpholides) for pyrrolizinecarboxylic acid esters, orby Friedel-Crafts aroylation.

In the modified Vilsmeier-Haack aroylation, the pyrrolizinecarboxamide(4) is treated with a mixture of a N,N-disubstituted benzamide such asN,N-dibutylbenzamide, benzmorpholide, or benzoylpiperidine, and an acidchloride, such as oxalyl chloride or phosphorus oxychloride, in anorganic solvent, typically a hydrocarbon solvent such as toluene, andthe solution is stirred for several hours at elevated temperatures,preferably about 35° C. to 65° C., more preferably about 40° C. to 60°C., especially about 40° C. The solution is stirred for several hours atroom temperature and an aqueous alkali metal hydroxide solution isadded. Suitable alkali metal hydroxides include lithium hydroxide,sodium hydroxide, and potassium hydroxide. The two-phase mixture isstirred, heated to about 55° C. to 85° C., preferably about 70° C. to75° C., and the layers separated. The resultant ketorolac-amide (6) maybe recovered from the organic layer by acidification with a mineralacid, filtered, and concentrated under vacuum.

In a Friedel-Crafts aroylation, the pyrrolizinecarboxamide (4) is heatedto elevated temperature, e.g. reflux temperature, in the presence of analkali metal carbonate or bicarbonate such as lithium carbonate orlithium bicarbonate, and an organic solvent such as toluene. Benzoylchloride is added and the mixture is heated for 6 hours to 8 hours. Oncethe reaction is complete, the reaction mixture is cooled to 70° C. to80° C., and crystallization of the resulting ketorolac-amide (6) may beeffected by addition of hexane; or the resulting ketorolac-amide (6) maybe isolated from the reaction mixture in a similar manner to thatdescribed above.

The ketorolac-amides (6) are novel, and are useful as intermediates inpreparing ketorolac and its pharmaceutically acceptable salts, which aretherapeutically useful as discussed above.

In step 5, the ketorolac-amide (6) is hydrolyzed to ketorolac (I);preferably by alkaline hydrolysis using an strong base in an alkanol.The reaction mixture is kept at elevated temperatures, such as at thereflux temperature of the alkanol, e.g. 65° C. for the preferredmethanol, for several hours, and then cooled. The ketorolac of formula Imay then be isolated by conventional techniques, such as addition ofwater, extraction with an organic solvent, separation of layers andacidification with a mineral acid, filtered and purified.

Ketorolac (I) may be isolated as the acid, if desired, but willpreferably be isolated as a pharmaceutically acceptable salt, especiallyas the tromethamine salt. The preparation and isolation of ketorolacsalts may be performed by conventional methods, such as by treating theketorolac (acid) with the appropriate base, preferably tromethamine, inan alkanol. The solution is concentrated by partial removal of thealkanol and the product crystallized by the addition of an organicsolvent such as ethyl acetate, cooled, filtered, and dried.

The invention is further illustrated, without limitation, by thefollowing example.

Preparation of 2-Bromo-4-chloro-N-methyl-N-phenylbutanamide (a compoundof Formula 2)

4-Chlorobutanoyl chloride (62 g, 440 mmol) and phosphorus tribromide (3g) were added to a distillation flask, and heated to 90° C. Bromine (25mL, 77.5 g, 485 mmol) was added slowly over eight hours, with thesolution being allowed to decolorize between additions. The acid gasesevolved were scrubbed with aqueous alkali. After the addition wascomplete, and the solution decolorized, a vacuum was slowly applied, andthe acid gases and phosphorus tribromide scrubbed. Unreacted startingmaterial was distilled at approximately 98° C. to 100° C./22 mmHg; andthe temperature slowly increased to 105° C., where a mixture of2-bromo-4-chlorobutanoyl chloride and 2-bromo-4-chlorobutanoyl bromidebegan to distill. Pure 2-bromo-4-chlorobutanoyl bromide distilled atapproximately 108° C. The combined yield of 2-bromo-4-chlorobutanoylchloride and 2-bromo-4-chlorobutanoyl bromide was 100.5 g, with abromide/chloride ratio of approximately 6:1. The mixture of2-bromo-4-chlorobutanoyl bromide and chloride is directly usable in thepreparation of the butanamide, if desired, or may be separated andeither component used.

2-Bromo-4-chlorobutanoyl bromide (80.3 g, 300 mmol) was slowly added toa solution of N-methylaniline (34.5 g, 320 mmol) and triethylamine (33.5g, 330 mmol) in toluene (340 mL). The reaction was exothermic, and themixture was cooled to maintain the temperature at about 40° C. After theaddition was complete, the resulting thick mixture was stirred for 30minutes, 150 mL water was added, and the mixture was stirred further.The aqueous and organic phases were separated, and the organic phase waswashed with 5% hydrochloric acid and with water. The toluene wasevaporated completely under slight vacuum to yield 86.3 g2-bromo-4-chloro-N-methyl-N-phenylbutanamide (98% yield, approximately95-96% pure). The triethylamine may be recovered from the aqueous phaseby addition of base and separation.

Preparation of 4-Chloro-N-methyl-N-phenyl-2-(2-pyrrolyl)butanamide (acompound of formula 3) in Butyl Diglyme

A solution of methylmagnesium chloride in butyl diglyme (4.0 L×2.8 M,11.2 mol, 2.8 equivalents with respect to2-bromo-4-chloro-N-methyl-N-phenylbutanamide) was added to a 12 L4-necked round bottom flask fitted with a mechanical stirrer and two 1 Laddition funnels, under a nitrogen atmosphere.2-Bromo-4-chloro-N-methyl-N-phenyl-butanamide (1.158 kg, 3.98 mol) wasadded to the first addition flask, and pyrrole (0.840 L, 0.812 kg, 12.1mol, 3.04 equivalents with respect to2-bromo-4-chloro-N-methyl-N-phenyl-butanamide) was added to the second.The pyrrole was slowly added to the methyl-magnesium chloride/butyldiglyme solution at 45° C. to 50° C. over 3 hours, and the reactionmixture was maintained at that temperature. The resulting viscousmixture was cooled to 25° C. and stirred for 30 minutes.2-Bromo-4-chloro-N-methyl-N-phenylbutanamide was added to the resultingmixture over a period of 2 hours while the temperature was maintained at25° C. to 30° C., and the resulting solution was stirred for another 3hours.

The dark-colored reaction mixture was transferred into 2.88 L (5.76 mol)2N hydrochloric acid with rapid stirring for 1 hour. The aqueous phasewas removed, and 0.8 L 15 weight % ammonium chloride in water was addedto the organic phase. The resulting mixture was stirred at 35° C. to 40°C. for 10 minutes, the aqueous phase then removed, and hexanes (2.4 L)added. The resulting suspension was cooled to −20° C. and maintained atthat temperature for a few minutes. The precipitate was filtered in a300 mL sintered glass funnel and washed with hexanes (1 L). Drying ofthe solid under vacuum at 25° C. to 30° C. yielded4-chloro-N-methyl-N-phenyl-2-(2-pyrrolyl)butanamide (90.84 g, 81 %yield).

Preparation of 4-Chloro-N-methyl-N-phenyl-2-(2-pyrrolyl)butanamide (acompound of formula 3) in Tetrahydrofuran/Toluene/Diglyme

Pyrrole (40 mL, 36.7 g, 557 mmol, 2.3 equivalents with respect to2-bromo-4-chloro-N-methyl-N-phenylbutanamide) was added dropwise to asolution of methylmagnesium chloride in tetrahydrofuran (180 mL×2.9 M,522 mmol, 2.1 equivalents) under a nitrogen atmosphere at a temperatureof 35° C. over a period of 30 minutes. Additional tetrahydrofuran (115mL) was added to the mixture. After the addition was complete, thesuspension was stirred at 25° C. for 30 minutes and then cooled to 15°C. to 20° C. A mixture of 2-bromo-4-chloro-N-methyl-N-phenylbutanamide(76.57 g, 249 mmol), toluene (90 mL), and diglyme (50 mL) was added tothe suspension in about 1 minute. The temperature increased from 30° C.to 35° C. in the first 30 minutes after addition. The resulting clearsolution was stirred for 3 hours to 5 hours at room temperature and thencooled to about 5° C.

Cooled hydrochloric acid (150 mL×2 N, 300 mmol), was added over 1 minuteto the reaction solution. The temperature of the suspension quicklyincreased to 30° C. to 35° C., and it was stirred for about 5 minutes.The resultant layers were separated and the organic layer was passedthrough a column of sodium hydroxide pellets. The eluent layer was againseparated. The combined organic layer was stirred overnight with sodiumcarbonate (2.64 g) at a temperature of −5° C., then distilled to recoverthe cosolvent and solvents. The residual dark suspension containing the4-chloro-N-methyl-N-phenyl-2-(2-pyrrolyl)-butanamide product was cooledto 25° C. and toluene (150 mL) was added. The resulting solution wasfiltered through an alumina column for decolorization and was useddirectly in the next step for the preparation ofN-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide.

Preparation ofN-Methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide (a compoundof formula 4)

A crude solution of 4-chloro-N-methyl-N-phenyl-2-(2-pyrrolyl)butanamidein toluene from the preceding step was added dropwise at 85° C. over 40minutes to 1 hour to a stirred suspension of ALIQUAT® 336 (2.01 g, 2 mol% with respect to pyrrolylbutanamide) and granular sodium hydroxide(29.9 g, 750 mmol, 3 equivalents) in toluene (50 mL). After the additionwas complete, the suspension was stirred under a nitrogen atmosphere ata temperature of 85° C. for 30 minutes, then cooled to 35° C. Cooledwater (200 mL) was rapidly added to the mixture and stirred for 15minutes at 25° C. The solution was rinsed with water and the layers wereseparated. The organic layer was washed with water (2×100 mL), thendistilled under atmospheric pressure to recover the toluene and water.The resultant solution was cooled to 50° C. and allowed to crystallizeafter the addition of hexane (2×50 mL) and a seed crystal. Thesuspension was cooled to 5° C. and stirred for 15 minutes. The resultantprecipitate was filtered, washed with 100 mL of hexane, and dried undervacuum at 25° C. to yield approximately 38 g (63%)N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide as a beigesolid. This solid was recrystallized from toluene (2-2.5 mL/g) to yieldlarge colorless crystals ofN-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide, mp 112° C.to 112.5° C.

Preparation of Benzoylpiperidine (a compound of formula 5)

Benzoyl chloride (500 mL, 606 g, 4.3 mol) was added dropwise to arapidly stirring mixture of piperidine (426 mL, 367 g, 4.3 mol), sodiumhydroxide (190 g, 4.7 mol, 1.1 equivalents), toluene (1 L), and water(1.7 L) over a period of 70 minutes. After the addition was complete,the mixture was stirred at 25° C. for one hour. The organic and aqueousphases were separated, and the organic phase was washed with 2Nhydrochloric acid (2×100 mL), concentrated by rotary evaporation, anddistilled under vacuum to yield benzoylpiperidine as a colorless liquidwhich crystallized on standing. (779 g, 95% yield, bp 169° C. to 171°C.).

Preparation of5-Benzoyl-N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide (acompound of Formula 6) using Benzoylpiperidine

N-Methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide (115.35 g,480 mmol) and toluene (100 mL) were added to a mixture ofbenzoylpiperidine (95.4 g, 1.05 equivalents) and phosphorus oxychloride(88 mL, 147 g, 0.96 equivalents), which had been stirred at 25° C. for 1hour. An additional 100 mL toluene was added. The suspension was heatedto a temperature of 40° C. to 45° C. for 4 hours. The resulting syrupwas transferred into a rapidly stirring solution of sodium hydroxide(180 g, 4.5 mol), piperidine (1.0 mL), and water (650 mL). Thetemperature was maintained at 25° C. to 35° C. and the mixture wasstirred for 1 hour. A mixture of toluene (100 mL), water (50 mL), andsodium hydroxide (12 g, 300 mmol) was added to the reaction flask, andthe entire reaction mixture was stirred at 25° C. for 1 hour. Thesuspension was then heated to 75° C. and the layers were separated. Theorganic layer was cooled to 60° C. and hexane (100 mL) was slowly added,and the solution slowly stirred and cooled to −15° C. The precipitatewas filtered, washed with toluene/hexane (150 mL, 2:1 v/v) and then withhexane (150 mL), and dried under vacuum at 25° C. to yield5-benzoyl-N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide(138.01 g, 83.5% yield).

Preparation of5-Benzoyl-N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide (acompound of formula 6) using Benzoyl Chloride

N-Methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide (52 g, 216mmol), lithium carbonate (24 g, 325 mmol, 1.5 equivalents), and toluene(155 mL) were heated to a reflux temperature of 100° C. to 105° C.Benzoyl chloride (37.5 g, 267 mmol, 1.25 equivalents) was added, and theentire reaction mixture was allowed to reflux for an additional 6 hoursto 8 hours. Once the reaction was complete, the mixture was cooled to70° C. to 80° C., lithium carbonate was filtered off and the filter cakewashed with 100 mL warm toluene, and the combined filtrate and washingswere seeded with a few crystals of5-benzoyl-N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide.Hexane (100 mL) was added to the warm toluene solution to effectcrystallization, and the mixture was stirred for 30 minutes; thenanother 80 mL of hexane was added. The mixture was stirred for 1 hour to2 hours at room temperature, cooled to 0° C. to 5° C., filtered, washedwith hexane (150 mL) and dried under vacuum at 60° C. to 70° C. to yield5-benzoyl-N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide(61.7 g, 82.8% yield).

Preparation of ketorolac and ketorolac tromethamine

A mixture of 34.4 g (100 mmol)5-benzoyl-N-methyl-N-phenyl-2,3-dihydro-1H-pyrrolizine-1-carboxamide, 25g sodium hydroxide in 25 mL water, and 80 mL methanol was refluxed for 5hours. The mixture was cooled to room temperature, stirred undernitrogen for sixteen hours, and then diluted with 80 mL of water. Themixture was extracted with toluene (2×50 mL), and the aqueous andorganic phases were separated. The aqueous phase was acidified with 6 Nhydrochloric acid (110 mL). The resulting precipitate was extractedseveral times with dichloromethane (1×150 mL), (1×75 mL), (1×50 mL). Thecombined extract was treated with FILTROL® (activated clay decolorizingagent) (4.5 g) for 30 minutes, filtered, and concentrated by atmosphericdistillation. Hexane (190 mL) was added and the entire mixture allowedto cool to room temperature and then further cooled to 0° C. to −5° C.The product, 5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acid(ketorolac) was collected by filtration, washed with 100 mL ofhexane/dichloromethane (7:3 v/v), and dried at 60° C. to 70° C. undervacuum, to yield ketorolac (21.3 g, 83.4% yield), mp 152° C. to 162° C.

Ketorolac (25 g) and 11.9 g tromethamine were dissolved in 175 mLmethanol. The solution was filtered and the filter washed with 40 mLmethanol. The resulting solution was concentrated by vacuumdistillation. Ethyl acetate (1×172 mL), (1×200 mL) was added to thesolution to precipitate the ketorolac tromethamine; and the solution wascooled to room temperature for two hours, cooled further to 0° C., andfiltered. The precipitate was washed with ethyl acetate/methanol (4:1v/v) and dried under vacuum at a temperature of approximately 65° C., toyield ketorolac tromethamine (35.0 g, 95% yield).

While this invention has been described in conjunction with specificembodiments and examples, it will be evident to one of ordinary skill inthe art, having regard to this disclosure, that equivalents of thespecifically disclosed materials and techniques will also be applicableto this invention; and such equivalents are intended to be includedwithin the following claims.

What is claimed is:
 1. A process for preparing ketorolac of formula (I),

comprising hydrolyzing a compound of the formula

where R¹ is alkyl and R² is optionally substituted phenyl, with a strongbase.
 2. The process of claim 1 where R¹ is methyl.
 3. The process ofclaim 1 where R² is phenyl.
 4. The process of claim 1 where the strongbase is an alkali metal hydroxide.
 5. The process of claim 1 where thestep of hydrolyzing is carried out in an alkanol.
 6. The process ofclaim 5 where the alkanol is methanol.
 7. The process of claim 1 furthercomprising the formation of a pharmaceutically acceptable salt ofketorolac by reaction of the ketorolac with a pharmaceuticallyacceptable base.
 8. The process of claim 7 where the pharmaceuticallyacceptable base is tromethamine.